1. Field of the Invention
The present invention generally relates to a manufacturing method of an optical waveguide, the optical waveguide, and an optical reception/transmission apparatus.
2. Description of the Related Art
Recently, operation speed (operation clock) of a central processing unit (CPU) or the like has been increased with increase in density of internal electrodes of an integrated circuit. On the other hand, signal transmission speed based on an electrical transmission method has almost reached a maximum limit, which becomes a bottleneck of the processing speed of a CPU or the like. Further, problems such as crosstalk and electromagnetic interference (EMI) noise of a high density electrode have risen with the increase in the operation speed of a CPU or the like. A solution is required to reduce the noise.
An optical interconnection method (optical wiring method) using optical waveguides has been receiving attention as a method for solving the problems. The optical interconnection method is capable of performing a broadband transmission far better compared to the electrical transmission method. The optical interconnection method can be adapted to increase the processing speed and provide a signal transmission system using optical parts with a compact size and lower power consumption. Further, the crosstalk noise and EMI noise can be reduced.
FIG. 1 is a cross section showing an example of an optical reception/transmission apparatus 200 including an optical waveguide 100 of related art. Referring to FIG. 1, the optical reception/transmission apparatus 200 is formed by the optical waveguide 100, a light emitting element 201 including a light emitting part 201a, and a light receiving element 202 including a light receiving part 202a. The optical waveguide 100 includes a supporting substrate 101, a core layer 102, a clad layer 103, grooves 104 and 105, and metal layers 106 and 107. θ1 is 45 degrees.
In the optical waveguide 100, the core layer 102 and the clad layer 103 are formed on the supporting substrate 101. The clad layer 103 is formed by a first clad layer 103a and a second clad layer 103b. The core layer 102 and the clad layer 103 include the grooves 104 and 105 which are formed to penetrate the core layer 102 and the clad layer 103. The metal layer 106 is formed on a 45 degree inclined part of the groove 104 and the metal layer 107 is formed on a 45 degree inclined part of the groove 105.
The light emitting element 201 including the light emitting part 201a is formed above the groove 104 of the optical waveguide 100. The light receiving element 202 including the light receiving part 202a is formed above the groove 105 of the optical waveguide 100.
In the optical reception/transmission apparatus 200, light emitted from the light emitting part 201a of the light emitting element 201 enters the optical waveguide 100 and a propagation direction of the light is changed by 90 degrees with the metal layer 106 as indicated by arrows in FIG. 1, and then the light enters the core layer 102. A refractive index of the core layer 102 is designed to be higher than that of the clad layer 103, so that the light entering the core layer 102 propagates within the core layer 102 without transmitting through the clad layer 103.
The light propagating within the core layer 102 reaches the metal layer 107. The propagation direction of the light is changed by 90 degrees with the metal layer 107 and enters the light receiving part 202a of the light receiving element 202. In this way, the metal layer 106 and the metal layer 107 formed on the 45 degree inclined parts of the groove 104 and the groove 105 function as direction changing parts of light propagation direction.
The optical waveguide 100 of FIG. 1 is manufactured by which the core layer 102 and the clad layer 103 are formed on the supporting substrate 101, and the groove 104 and the groove 105 having 45 degree inclined parts penetrating the core layer 102 and the clad layer 103 are formed. Further, the metal layers 106 and 107 are formed on the 45 degree inclined parts of the core layer 102 and the clad layer 103.
The grooves 104 and 105 having the 45 degree inclined parts may be formed by a dicing process, a die imprinting or the like. Also, as another forming method of the grooves 104 and 105, it has been proposed that a dry etching method is conducted to perform patterning with a photoresist mask having mask patterns in which sizes of openings or density of the openings are gradually increased or reduced in a longitudinal direction of the optical waveguide 100. Further, as another forming method of the grooves 104 and 105, it has been proposed that a photo mask for forming the core layer 102 is separated from a surface of the material of the core layer 102 more than approximately 500 μm and exposed by light so that light diffraction for curing material is controlled.
With respect to another optical waveguide, it has been proposed to use mirror members having mirror surfaces instead of the grooves 104 and 105 and the metal layers 106 and 107 of the 45 degree inclined parts of the optical waveguide 100. These optical waveguides can be manufactured by curing liquid state material forming the optical waveguide in which the mirror members having mirror surfaces are imbedded in the manufacturing process of the optical waveguide.
Patent document 1: Japanese Patent Application Publication No. H6-265738
Patent document 2: Japanese Patent Application Publication No. 2001-272565
Patent document 3: Japanese Patent Application Publication No. 2002-131586
Patent document 4: Japanese Patent Application Publication No. 2007-183467
Patent document 5: Japanese Patent Application Publication 2007-183468
In a manufacturing method of the optical waveguide 100 of a related art, after forming the 45 degree inclined parts of the groove 104 and the groove 105, a forming process of the metal layers 106 and 107 is necessary after forming the grooves 104 and 105 having the 45 degree inclined parts by a sputtering method, a nonelectrolytic plating method or the like. This method has been a problem because the manufacturing process is complicated.
The problem is that a mask for forming partial parts of the metal layers 106 and 107 is necessary in a process of forming the metal layers 106 and 107 on the 45 degree inclined parts, because it is difficult to perform alignment between the mask and the microstructured 45 degree inclined parts of the grooves 104 and 105.
Further, when the mirror members having mirror surfaces are used instead of the grooves 104 and 105 and the metal layers 106 and 107 of the 45 degree inclined parts of the optical waveguide 100, the material used for the optical waveguide is limited to liquid state material. In this case, film shape material cannot be used. Thus, there has been a problem that a film material cannot be used.